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Title: Crystal structure, chemical expansion and phase stability of HoMnO{sub 3} at high temperature

Abstract

Anisotropic thermal and chemical expansion of hexagonal HoMnO{sub 3} was investigated by high temperature X-ray diffraction in inert (N{sub 2}) and oxidizing (air) atmospheres up to 1623 K. A second order structural phase transition directly from P6{sub 3}cm to P6{sub 3}/mmc was found at 1298{+-}4 K in N{sub 2} atmosphere, and 1318{+-}4 K in air. For the low temperature polymorph P6{sub 3}cm the contraction of the c-axis was more rapid in inert than in oxidizing atmosphere. The c-axis of the P6{sub 3}/mmc polymorph of HoMnO{sub 3} displayed anomalously high expansion above 1400 K, which is discussed in relation to chemical expansion caused by point defects. The a-axis expanded stronger in inert than oxidizing atmosphere. Anisotropic chemical and thermal expansion of the P6{sub 3}cm phase of YMnO{sub 3} in N{sub 2}, air and O{sub 2} atmospheres was found to be qualitatively similar to that of HoMnO{sub 3}. Decomposition of hexagonal HoMnO{sub 3} by two different processes occurs in oxidizing atmosphere above {approx}1200 K followed by nucleation and growth of the perovskite polymorph of HoMnO{sub 3}. A rapid, reconstructive transition from the perovskite back to the hexagonal polymorph was observed in situ at 1623 K upon reduction of the partial pressure ofmore » oxygen. A phase stability diagram of the hexagonal and orthorhombic polymorphs is proposed. Finally, distinctly non-linear electrical conductivity was observed for both HoMnO{sub 3} and YMnO{sub 3} in oxidizing atmosphere between 555 and 630 K, and shown to be associated with excess oxygen. - Graphical abstract: Chemical expansion of hexagonal HoMnO{sub 3} is observed during HTXRD in different pO{sub 2}. Oxidizing atmosphere favors the competing perovskite polymorph. Electrical conductivity anomalies related to excess oxygen are found at 550-630 K. Highlights: Black-Right-Pointing-Pointer Thermal evolution of crystal structure of HoMnO{sub 3} studied up to 1623 K in air and N{sub 2}. Black-Right-Pointing-Pointer Anisotropic chemical expansion of HoMnO{sub 3} and YMnO{sub 3} in N{sub 2}, air and O{sub 2}. Black-Right-Pointing-Pointer Hexagonal phase destabilized with respect to perovskite in oxidizing atmosphere. Black-Right-Pointing-Pointer Crystal structure and phase stability discussed in terms of point defect chemistry. Black-Right-Pointing-Pointer Electrical conductivity anomalies associated with excess oxygen at 550-630 K.« less

Authors:
; ; ; ;  [1]
  1. Department of Materials Science and Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway)
Publication Date:
OSTI Identifier:
22149978
Resource Type:
Journal Article
Journal Name:
Journal of Solid State Chemistry
Additional Journal Information:
Journal Volume: 196; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0022-4596
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANISOTROPY; DECOMPOSITION; ELECTRIC CONDUCTIVITY; HCP LATTICES; ORTHORHOMBIC LATTICES; OXYGEN; PARTIAL PRESSURE; PEROVSKITE; PHASE STABILITY; PHASE TRANSFORMATIONS; POINT DEFECTS; THERMAL EXPANSION; X-RAY DIFFRACTION

Citation Formats

Selbach, Sverre M., E-mail: selbach@material.ntnu.no, Nordli Lovik, Amund, Bergum, Kristin, Tolchard, Julian R., Einarsrud, Mari-Ann, and Grande, Tor. Crystal structure, chemical expansion and phase stability of HoMnO{sub 3} at high temperature. United States: N. p., 2012. Web. doi:10.1016/J.JSSC.2012.07.024.
Selbach, Sverre M., E-mail: selbach@material.ntnu.no, Nordli Lovik, Amund, Bergum, Kristin, Tolchard, Julian R., Einarsrud, Mari-Ann, & Grande, Tor. Crystal structure, chemical expansion and phase stability of HoMnO{sub 3} at high temperature. United States. doi:10.1016/J.JSSC.2012.07.024.
Selbach, Sverre M., E-mail: selbach@material.ntnu.no, Nordli Lovik, Amund, Bergum, Kristin, Tolchard, Julian R., Einarsrud, Mari-Ann, and Grande, Tor. Sat . "Crystal structure, chemical expansion and phase stability of HoMnO{sub 3} at high temperature". United States. doi:10.1016/J.JSSC.2012.07.024.
@article{osti_22149978,
title = {Crystal structure, chemical expansion and phase stability of HoMnO{sub 3} at high temperature},
author = {Selbach, Sverre M., E-mail: selbach@material.ntnu.no and Nordli Lovik, Amund and Bergum, Kristin and Tolchard, Julian R. and Einarsrud, Mari-Ann and Grande, Tor},
abstractNote = {Anisotropic thermal and chemical expansion of hexagonal HoMnO{sub 3} was investigated by high temperature X-ray diffraction in inert (N{sub 2}) and oxidizing (air) atmospheres up to 1623 K. A second order structural phase transition directly from P6{sub 3}cm to P6{sub 3}/mmc was found at 1298{+-}4 K in N{sub 2} atmosphere, and 1318{+-}4 K in air. For the low temperature polymorph P6{sub 3}cm the contraction of the c-axis was more rapid in inert than in oxidizing atmosphere. The c-axis of the P6{sub 3}/mmc polymorph of HoMnO{sub 3} displayed anomalously high expansion above 1400 K, which is discussed in relation to chemical expansion caused by point defects. The a-axis expanded stronger in inert than oxidizing atmosphere. Anisotropic chemical and thermal expansion of the P6{sub 3}cm phase of YMnO{sub 3} in N{sub 2}, air and O{sub 2} atmospheres was found to be qualitatively similar to that of HoMnO{sub 3}. Decomposition of hexagonal HoMnO{sub 3} by two different processes occurs in oxidizing atmosphere above {approx}1200 K followed by nucleation and growth of the perovskite polymorph of HoMnO{sub 3}. A rapid, reconstructive transition from the perovskite back to the hexagonal polymorph was observed in situ at 1623 K upon reduction of the partial pressure of oxygen. A phase stability diagram of the hexagonal and orthorhombic polymorphs is proposed. Finally, distinctly non-linear electrical conductivity was observed for both HoMnO{sub 3} and YMnO{sub 3} in oxidizing atmosphere between 555 and 630 K, and shown to be associated with excess oxygen. - Graphical abstract: Chemical expansion of hexagonal HoMnO{sub 3} is observed during HTXRD in different pO{sub 2}. Oxidizing atmosphere favors the competing perovskite polymorph. Electrical conductivity anomalies related to excess oxygen are found at 550-630 K. Highlights: Black-Right-Pointing-Pointer Thermal evolution of crystal structure of HoMnO{sub 3} studied up to 1623 K in air and N{sub 2}. Black-Right-Pointing-Pointer Anisotropic chemical expansion of HoMnO{sub 3} and YMnO{sub 3} in N{sub 2}, air and O{sub 2}. Black-Right-Pointing-Pointer Hexagonal phase destabilized with respect to perovskite in oxidizing atmosphere. Black-Right-Pointing-Pointer Crystal structure and phase stability discussed in terms of point defect chemistry. Black-Right-Pointing-Pointer Electrical conductivity anomalies associated with excess oxygen at 550-630 K.},
doi = {10.1016/J.JSSC.2012.07.024},
journal = {Journal of Solid State Chemistry},
issn = {0022-4596},
number = ,
volume = 196,
place = {United States},
year = {2012},
month = {12}
}